Abstract Supportive relationships with parents are paramount for psychological well-being among lesbian, gay and bisexual (LGB) youth, who often face adverse psychological outcomes as a result of their stigmatized identity (D'Augelli &Hershberger, 1993;Goldfried &Goldfried, 2001). Little is known, however, about other family-based factors that may be related to parental acceptance and psychological functioning among LGB youth. Similarly, little is known about how a parent's own well-being may be affected by having an LGB child. The present study utilizes Family Stress Theory (Hill, 1949;McCubbin &Patterson, 1985), a widely used systems-based framework, to formulate and test both cross-sectional and longitudinal models predicting psychological functioning among LGB youth and their parents. Participants will include 150 self-identified LGB youth (ages 16 to 21 at baseline) and at least one parent. Youth and parents will complete questionnaires assessing family resources, beliefs about sexuality, pile-up of stressors, parental acceptance of the youth's sexual orientation, and a range of parent and child mental health outcomes. A structured problem-solving discussion between parents and their child will be videotaped and coded to assess aspects of parent-child relationship functioning and communication. The current study is a longitudinal one, in which families will be recruited to participate in four time points, including six, twelve, and eighteen months after initial participation. Structural equation modeling will be used to test theory-based cross-sectional models in which family stress factors, including family resources, beliefs about sexuality, and pile-up of family stressors, are related to youth and parent psychological functioning, mediated by parental acceptance of a child's sexual orientation. In complex mediational models, parent-child relationship quality will be tested as a link between family stress factors and parental acceptance. Latent growth curve modeling will be employed to test longitudinal models based on family stress theory predicting outcome from baseline functioning and changes over time in study measures, including changes in parental acceptance over time. Analyses will also be conducted to examine differences in growth trajectories across time based on child gender and family ethnicity. This study is among the first to apply a family systems approach to mental health among sexual minority youth. It is also among the first to include both sexual minority youth and their family members as participants and is the first to observationally examine relational patterns in families of sexual minority youth, particularly in a cross-ethnic sample. Empirically-based models are essential in formulating effective mental health services for sexual minority youth and their families. Findings from this project will provide insight into factors promoting supportive family relationships and healthy development among lesbian, gay, and bisexual youth and their parents. PUBLIC HEALTH RELEVANCE: The current study is proposed as a longitudinal examination of family systems factors related to parental acceptance of youth disclosures of sexual orientation, and how such factors, including parent-child relationship quality and parental acceptance, may be related to parent and child functioning over time. This study focuses on a group of youth at high risk due to sexual minority status and examines pathways related to social and emotional functioning in both young women and men across different ethnic groups. This study is relevant to public health in that it focuses on an at risk group of youth and seeks to understand how family factors may be related to both adjustment and high risk behaviors in these youth over time.